Title : Modelling thermokinetics using the sestak-berggren equation: A calcium carbonate case study
During the production of catalysts there are many energy-intensive thermal processing steps, and these can be critical to both the performance of the final product and the economics of the manufacturing process. To design efficient, specialised calcination and drying processes for new catalyst products, kinetic information must be extracted from thermal analysis data.
This presentation will discuss the methodology developed to extract kinetic parameters from thermal analysis data using the Sestak-Berggren equation, specifically the decomposition of calcium carbonate studied through thermogravimetric analysis. The thermal decomposition of calcium carbonate has been selected as a case study, as calcium carbonate is an industrially relevant mineral and the product calcium oxide can be used as a carbon dioxide capture material.
The Sestak-Berggren equation is a mathematical model which describes the behaviour of solid-state reaction mechanisms, many of which occur during the thermal processing of a material. The parameters estimated from the Sestak-Berggren equation are used to inform which of these solid-state mechanisms are occurring. Models for these mechanisms, such as three-dimensional diffusion, can also be found in the literature.
Initially conventional kinetic experiments were completed, varying the temperature ramp rate. Parameter estimation was carried out using Athena Visual Studio, along with the statistical analysis of the quality of fit. Following the results of the Sestak-Berggren modelling, discrimination between candidate mechanistic models was completed. It was found that the decomposition of calcium carbonate is dominated by a two-dimensional interphase-controlled mechanism.
This case study further utilises design of experiments to explore the impact of temperature ramp rate, space velocity and particle Reynolds number. It was found that the particle Reynolds number had minimal impact on the results, however the ramp rate and space velocity do have an impact on the regime encountered. The problems associated with including the space velocity will be discussed and possible improvements highlighted.
Audience Take Away:
- This presentation will outline a method for extracting kinetic information from thermogravimetric analysis data, specifically using the Sestak-Berggren equation to inform the mechanism occurring during a decomposition reaction.
- The presentation will highlight the use of statistical model discrimination in thermal analysis.
- The value that the use of design of experiments can bring to a kinetic study.
- The problems which arise when space velocity is considered in thermogravimetric analysis experiments.